Sealing member and capped bearing

ABSTRACT

Sealing members, such as rolling bearing seal and oil seal, which are not only satisfactory in the fundamental properties required of them, such as sealing performance, heat resistance, mechanical strength and oil resistance, but also excellent in creep and PAG resistances. The member has an elastic part and is made by molding a modified nitrile rubber comprising a butadiene-acrylonitrile-acrylate copolymer and containing an organic peroxide as a vulcanizer, a metal oxide as a vulcanization aid, and a basic silicate as a reinforcing filler.

TECHNICAL FIELD

The present invention relates to a sealing member such as a rollerbearing seal, an oil seal or the like to be used in automotivecomponents such as engines and related equipment, driving shafts,wheels, power steerings, etc., and household electrical appliance partssuch as compressor rotary shafts etc., for instance, and to a sealedbearing having said sealing member.

BACKGROUND ART

As far as sealing members, such as roller bearing seals and oil seals,which are used in sealed bearings and the like to prevent the rotaryshaft lubricating oil from leaking and for the like purposes areconcerned, various contrivances have been made for their sealingproperty which is their primary function, and for maintaining itsproperty. To roller bearing seals and oil seals for rotary shafts to beused in automotive components, household electrical appliance parts andthe like, heat resistance enabling long-term service as well asdurability and oil resistance at the surface of contact is essential inorder that the sealing property may be maintained for a long time.

The roller bearing seals and oil seals which are used in the automotiveengine and related equipment, e.g. the transmission, axles, etc., aregenerally maintained at 120 to 130° C. while the automobiles arerunning. However, when the car stops because of a traffic congestion,for instance, the effect of air cooling diminishes, allowing the sealtemperature to exceed 150° C. at intervals. Therefore, heat resistanceis an important requisite for assuring the mechanical strength. Thewater pump bearing seal, alternator bearing seal, wheel system seal,etc. are liable to be exposed to rain water (in some instances, saltwater and muddy water), radiator water (LLC-containing water), etc.,hence sufficient water resistance is essential.

In the case of bearing seals and oil seals to be used in the automotivetransmission, transaxle, differentials and the like, not onlyfunctionally sufficient mechanical strength but also high heatresistance is required in order that they may serve the purposecontinuously in the lubricating oil environment of 130 to 140° C. at themaximum. Furthermore, a contrivance is required for preventingcontaminants in the lubricating oil from entering the bearings andfurther for reducing seal lip abrasion due to the contaminants. Thus, inaddition to said mechanical strength and heat resistance, good creepresistance (CS) is essential.

In the case of sealing members to be used in automotive power steeringsand the like, still higher mechanical strength is essential forresisting the high internal pressure, in addition to the above-mentionedheat resistance.

In the case of bearing seals and oil seals to be used in the automotivecrankshaft, cam shaft and the like, a low-aniline-point performance isessential for resisting the engine oil or fuel oil which has theproperty to swell rubber, in addition to the above-mentioned heatresistance.

In the case of the bearing seal or oil seal for the compressor as acomponent of the automotive air conditioner, household or office airconditioner, refrigerator or the like, those conventional machine oilsfor compressor use which are based on mineral oils are being switchedover to a synthetic lubricating oil polyalkylene glycol (PAG), from theviewpoint of compatibility with a substitute fluorocarbon, which hasrecently been used as a heating medium in lieu of the fluorocarbon whichtends to destroy the ozone layer. Thus, Japanese Kokai PublicationHei-3-160186 discloses a technology of improving compressors using PAGas the lubricating oil and Japanese Kokai Publication Hei-3-281688discloses a technology of using PAG as a synthetic lubricating oil inthe refrigerating machine. PAG may gasify (as a volatilized oil or amist) during use. In that case, the gasified PAG and air come intosimultaneous contact with the bearing seals or oil seals, so that it isessential that these have sufficient PAG resistance.

Meanwhile, nitrile rubbers (NBRs) having good oil resistance have so farbeen used as the material for the above-mentioned bearing seals or oilseals. However, NBRs fail to satisfy the heat resistance requirement.For instance, they are not suited for use in the vicinity of an enginewhere the temperature may rise to about 150° C. The use of hydrogenatedNBRs (HNBRs) as alternatives was considered. However, they areexpensive, hence the use thereof presents a problem from the economicviewpoint.

Therefore, the use of acrylic rubbers (ACMs) or fluoro rubbers (FKMs)has been proposed. However, ACMs are disadvantageous from mechanicalstrength and oil resistance viewpoints and FKMs have drawbacks in thatthey are expensive and, hence, uneconomical.

A technology of incorporating a certain amount of a (meth)acrylate inbutadiene and acrylonitrile which are components of the NBRs, to givemodifiled nitrile rubbers with improved processability is disclosed inU.S. Pat. No. 2,395,017. Japanese Kokoku Publication Sho-47-21579discloses a technology of copolymerizing butadiene, acrylonitrile,chloroacrylonitrile and an alkyl acrylate to give a modified nitrilerubber with improved heat resistance. Japanese Kokoku PublicationSho-60-11744 discloses a technology of copolymerizing a conjugateddiene, an unsaturated nitrile and an unsaturated dicarboxylic acid esterand incorporating a specific additive in the copolymer to provide thesame with heat resistance.

In Japanese Kokoku Publication Sho-62-59138, there is disclosed atechnology of incorporating a vulcanization agent and a crosslinkingagent in a modified nitrile rubber with a limited Mooney viscosity asobtained by specifying the proportions of the constituents, namelybutadiene, acrylonitrile and a hydroxyalkyl (meth)acrylate, to therebyinsure processability.

In the case of sealed roller bearings, which support rotating shafts incompressors, too, attention has so far been paid only to the use, as thematerial for sealing plates, of a material excellent from thelubrication and heat resistance viewpoints. Thus, from the costviewpoint as well, the use of acrylic rubber materials and the like, forinstance, has been preferred.

The grease so far used as a lubrication medium in bearings is composedof a poly-α-olefin base oil and, as a thickening agent, diurea.Therefore, EPDMs or chlorinated polyethylene (CM), though resistant toPAGs, has not been regarded as being suited as the sealing platematerial mentioned above.

When a PAG is used as the lubricating oil in a compressor, for examplein a swash type rotary compressor (FIG. 2), the lubricating oil PAGsealed in a cavity 11 of a sealed vessel 10 contributes to lubricationof the swash plate during rotation. However, at high temperaturesencountered, for instance, when the compressor is used in an automotiveair conditioner, the PAG is gasified and the gas goes through theclearance within the vessel and arrives at the roller bearing 12 on therotary shaft 13. Once the PAG gas has arrived at the roller bearing 2(FIG. 1), the sealing plates 5 and 6 which seal the roller bearing 2 arein contact with air at all times, and the sealing plates 5 and 6 comeinto a state of simultaneous contact with air and PAG gas.

Under such circumstances, due to simultaneous contact of the sealingplates with air and PAG gas, the sealing plates made of an acrylicrubber, which has previously been used for a urea-type grease, havepresented problems, namely corrosion and deterioration.

To solve the above problems, an attempt was made to use nitrile rubbers(NBRs), which have a PAG-resistant characteristic, as materials for thesealing plates mentioned above. NBRs are also resistant to mineraloil-based greases, hence are suited for that purpose. However, theirheat resistance, as determined in a heat aging test in air, is at mostabout 125° C. Thus, there is a problem that NBRs cannot be used inautomotive air conditioners where a heat resistance of 130 to 150° C. isrequired.

It is conceivable to use hydrogenated NBRs in lieu of NBRs. However,though they solve the heat resistance problem, they raise the costmarkedly, hence they can hardly be put to practical use.

DISCLOSURE OF THE INVENTION

None of the technologies mentioned above are directed to the developmentof a material that could be used for bearing seals or oil seals, andthey have so far failed to satisfy the heat resistance, oil resistance,creep resistance, PAG resistance, and other requirements which areimposed on bearing seals or oil seals.

In view of the foregoing, it is a primary object of the presentinvention to provide a sealing member, such as a roller bearing seal oran oil seal, which satisfies those fundamental properties which aregenerally imposed thereon, namely the sealing property, heat resistance,mechanical strength and oil resistance requirements, and which is, inaddition, excellent in creep resistance and PAG resistance.

Thus, according to the present invention, the sealing member has anelastic part formed by molding a modified nitrile rubber of thebutadiene-acrylonitrile-acrylate type which contains an organic peroxideas a vulcanization agent, a metal oxide as a vulcanization acceleratorand a basic silicic acid as a reinforcing filler.

The modified nitrile rubber to be used according to the presentinvention is a modification product of NBR as obtained by partlyreplacing the monomer component of NBR polymer with an acrylate((meth)acrylic ester) which is inherently a constituent monomer ofacrylic rubber.

The modified nitrile rubber to be used according to the presentinvention comprises the acrylonitrile and butadiene components asconstituent monomers, as in the conventional NBR species.

However, the modified nitrile rubber to be used according to the presentinvention comprises, in addition to the above-mentioned acrylonitrileand butadiene components, an acrylate component as a further constituentmonomer. This acrylate component is not limited to any particularspecies provided that it can be used in the modified nitrile rubber.Thus it includes, among others, (meth)acrylic esters, such as ethylacrylate, propyl acrylate, butyl acrylate, ethyl methacrylate, propylmethacrylate, butyl methacrylate, β-hydroxyethyl acrylate,β-hydroxypropyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropylmethacrylate, β-hydroxypropyl acrylate, etc.

In the modified nitrile rubber to be used according to the presentinvention, the proportions of the acrylonitrile and butadiene componentsare preferably approximately the same as those in ordinary NBR species.Thus, for example, the acrylonitrile component preferably accounts forabout 1 to 50% by weight and the butadiene component for about 1 to 98%by weight, while the content of said acrylate component is preferably 1to 90% by weight. It is necessary, however, that the total content ofthe acrylonitrile and butadiene components in the modified nitrilerubber should amount to not less than 50% by weight. In the case ofcompressor sealing members for which particular consideration is to begiven to PAG resistance, the content of the acrylate component mentionedabove preferably amounts to 1 to 15% by weight, more preferably 5 to 10%by weight. When the proportion of said acrylate component is less than1% by weight, the modified nitrile rubber will be insufficient in heatresistance, mechanical strength, oil resistance, creep resistance andPAG resistance, whereas when the content of the acrylate componentexceeds 15% by weight, the sealing member will no longer have thefundamental properties required; thus, in either case, the object of thepresent invention cannot be accomplished.

The modified nitrile rubber to be used in the present invention issubjected to vulcanizing reaction with a combination of a metal oxideand an organic peroxide, without using any sulfur base vulcanizationagent which is generally used in vulcanizing NBR.

As said metal oxide, there may be mentioned, among others, magnesiumoxide and the like. Magnesium oxide is particularly preferred for thepurpose of the present invention. The metal oxide is used preferably inan amount of 5 to 20 parts by weight, more preferably 6 to 10 parts byweight, per 100 parts by weight of the modified nitrile rubber.

The organic peroxide mentioned above includes, but is not limited to,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,2'-bis(t-butylperoxy)-p-diisopropylbenzene, dicumyl peroxide,di-t-butyl peroxide, t-butyl benzoate, 1,1-bis(t-butyl-peroxy)-3,3,5-trimethylcyclohexane, 2,4-dichlorobenzoylperoxide, benzoyl peroxide, p-chlorobenzoyl peroxide, t-butylperoxybenzoate, and di-t-butylperoxyisophthalate, among others. Amongthem, dicumyl peroxide is preferred.

The organic peroxide also mentioned above is used preferably in anamount of 1 to 10 parts by weight, more preferably in an amount of 2 to5 parts by weight, per 100 parts by weight of the modified nitrilerubber.

In the practice of the present invention, a basic silicic acid is usedas a reinforcing filler.

Silicic acid generally occurs as a solid acid and, in many cases, showsacidity and is scarcely soluble in water. On the contrary, the basicsilicic acid to be used according to the present invention shows abasicity of pH 7 to 10 in aqueous suspension. As such, there may bementioned, for example, silica (silica sand, diatomaceous earth,amorphous silica), synthetic silicic acid (white carbon) and, further,aluminum silicate (pyrophillite, kaolin), magnesium silicate (talc,finely divided talc), calcium silicate (Calsil HM700), aluminum sodiumsilicate (zeolex 23, HM500), calcium magnesium silicate, and the like.

Said basic silicic acid is recommendably used in an amount of 10 to 60parts by weight, preferably 30 to 50 parts by weight, per 100 parts byweight of the modified nitrile rubber.

In incorporating the above-mentioned metal oxide, organic peroxide, andbasic silicic acid in modified nitrile rubber in accordance with thepresent invention, other additives in common use, such as silanecoupling agents, crosslinking auxiliaries, etc., may be combinedly usedin appropriate proportions.

The sealing member of the present invention desirably has a (metal) casetherewithin. By this, the sealing member of the present inventionacquires rigidity, which is a characteristic required of the bearingseal and oil seal. The modified nitrile rubber having theabove-mentioned constitution according to the present invention is alsosuited for adhesion to the (metal) case mentioned above.

The sealing member of the present invention can be applied to all usesin which the sealing property, heat resistance, mechanical strength, oilresistance, creep resistance and PAG resistance are required. Thesealing member of the present invention, when it is of a type such thatthe seal itself is lubricated by the medium which is a sealed object(the so-called contact type) and when it is used under the conditions ofthe highest continuous working temperature of about 130° C. or thehighest intermittent working temperature of about 150° C., producesmarked effects.

The sealing member may also be of the non-contact type, however.

Typical examples of such use include, but are not limited to, sealedbearings. As uses of the sealing member of the present invention, theremay be mentioned, for example, sealing members for engines and relatedcomponents, such as water pump bearings, alternator bearings, tensionpulley bearings, crankshaft bearings, camshaft bearings, etc.; sealingmembers for use in drive shaft systems, such as center bearings,transmission bearings, and transmission-axle-transfer bearings; sealingmembers for wheel systems, such as bearing-integrated hub unit sealsetc.; sealing members for power steering systems, such as reciprocating(rod) seals, swing (pinion) seals; and sealing members for compressors,such as compressor seals etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a macrograph of a roller bearing.

FIG. 2 shows a cross section of a swash plate type rotary compressor.

FIG. 3 shows a cross section of an alternator bearing.

FIG. 4 shows a cross section of a water pump bearing.

FIG. 5 shows a cross section of a center bearing.

FIG. 6 shows a cross section of a wheel bearing.

FIG. 7 shows cross section of a tension pully bearing.

FIG. 8 shows a cross section of a crank bearing.

FIG. 9 shows a cross section of a steering rod seal.

FIG. 10 shows a cross section of a differential axle mechanism.

1 . . . an inner ring

2 . . . an outer ring

3 . . . a ball

4 . . . a cage, and

5 and 6 . . . sealing members and 8 . . . metal case.

BEST MODES FOR CARRYING OUT THE INVENTION

The following test examples are further illustrative of the presentinvention. In the test examples, measurements were made by the followingmethods.

Mechanical properties were evaluated and other tests were performedaccording to JIS K 6301.

The abrasion resistance test was performed using a Williams abrasiontester and the results obtained in the comparative examples wereexpressed in terms of relative abrasion loss with the abrasion loss inTest Example 1 according to the present invention being taken as 100. Inreporting the cost ratios for the comparative examples, the costrequired in Test Example 1 according to the present invention was takenas 1.

The components weighed according to each formulation shown in Table 1were kneaded on 6-inch rolls and test specimens were processed under thevulcanization conditions shown in Table 1. The results are shown inTable 2.

In Test Example 1 according to the present invention, neither thermalhardening nor dissolution occurred in any of the heat aging, oilresistance, PAG resistance and water resistance tests, the abrasionresistance was superior and the advantageousness from the viewpoint ofcost was proved, as compared with the comparative examples.

Further, comparative experiments were performed by adding variousvulcanization agents, vulcanization accelerators and reinforcing fillersto the modified NBR (JSR N640H, product of Japan Synthetic Rubber) usedin Test Example 1 according to the present invention. The componentscompounded and the vulcanization conditions used in Test Example 2 andComparative Examples 5 to 9 are shown in Table 3, and the resultsobtained are shown in Table 4.

The product of Test Example 2 was slightly inferior to that of TestExample 1 according to the present invention but produced no problem inthe use thereof. The products of Comparative Examples 5 to 9 wereinferior to those of Test Examples 1 and 2.

In Table 1 and Table 3, "JSR N640H" stands for a modified NBR producedby Japan Synthetic Rubber, "JSR N230S" for an NBR produced by JapanSynthetic Rubber, "Nipol AR-72" for an ACM produced by Nippon Zeon,"zetpol 2020" for a hydrogenated NBR produced by Nippon Zeon, "VitonE-430" for an FKM produced by Showa Denko Du Pont, "Nocrac CD" for anantioxidant produced by Ouchi Shinko Chemical Industrial Co., "NipsilER" for a neutral-basic silica species produced by Nippon SilicaIndustrial Co., "Carplex #1120" for a basic silica produced by Shionogi& Co., "Carplex XR" for an acidic silica species produced by Shionogi &Co., "Percumyl D-40" for an organic peroxide produced by Nippon Oil andFats, "Peroximon F-40" for an organic peroxide produced by Nippon Oiland Fats, "Kyowamag #150" for magnesium oxide produced by Kyowa ChemicalIndustry, "KBM503" for a silane coupling agent produced by Shin-EtsuChemical, and "Satintone No. 5" for an acidic calcined clay speciesproduced by Engelhard Minerals.

In the PAG resistance test referred to in Table 2, Nippon Denso's No. 8oil was used.

In Table 2, the evaluation criteria are as follows:

∘: Good;

Δ: Rather poor;

X: Poor

                                      TABLE 1                                     __________________________________________________________________________                Test Comparative                                                                         Comparative                                                                         Comparative                                                                         Comparative                                Component (weight parts)                                                                  Example 1                                                                          Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                                  __________________________________________________________________________    JSR N640H   100  --    --    --    --                                         JSR N230S   --   100   --    --    --                                         Nipol AR-72 --   --    100   --    --                                         Zetpol 2020 --   --    --    100   --                                         Viton E-430 --   --    --    --    100                                        Stearic acid                                                                              1    1     1     1     --                                         Nocrac CD   2    2     2     2     --                                         Hydrozincite #1                                                                           --   5     --    --    --                                         Reinforcing filler                                                            Nipsil ER   --   45    --    --    --                                         Carplex #1120                                                                             45   --    50    --    --                                         FEF carbon  --   --    --    50    --                                         MT carbon   --   --    --    --    30                                         Vulcanization agent                                                           Sulfur      --     0.5   0.3 --    --                                         Accelerator TT                                                                            --   2     --    --    --                                         Accelerator CZ                                                                            --   2     --    --    --                                         Sodium stearate                                                                           --   --    3     --    --                                         Potassium stearate                                                                        --   --      0.5 --    --                                         Percumyl D-40                                                                             3    --    --    --    --                                         Peroximon F-40                                                                            --   --    --    8     --                                         Vulcanization accelerator                                                     Kyowamag #150                                                                             10   --    --    --    3                                          Calcium hydroxide                                                                         --   --    --    --    6                                          KEM503      1    1     1     --    --                                         Plasticizer DOP                                                                           5    5     --    --    --                                         Vulcanization condition                                                       Primary press                                                                             180° C.                                                                     170° C.                                                                      180° C.                                                                      180° C.                                                                      180° C.                             vulcanization                                                                             5 min                                                                              3 min 3 min 5 min 5 min                                      Secondary oven                                                                            150° C.                                                                     --    150° C.                                                                      150° C.                                                                      230° C.                             vulcanization                                                                             4 hrs      4 hrs 4 hrs 24 hrs                                     __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                     Test Comparative                                                                         Comparative                                                                         Comparative                                                                         Comparative                                            Example 1                                                                          Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                             __________________________________________________________________________    Dry mechanical properties                                                     Hardness (JIS-A) 65   71    63    75    70                                    Tensile strength (MPa)                                                                         15.03                                                                              19.80 8.95  28.45 12.51                                 Elongation (%)   372  584   135   287   302                                   Heat aging test [Evaluation]                                                                   ∘                                                                      x     ∘                                                                       ∘                                                                       ∘                         (heating in air 150° C. × 70 hrs)                                Hardness change (pts.)                                                                         +12  +16   +2    +6    +1                                    Tensile strength change (%)                                                                    +2   -39   +3    -3    -3                                    Elongation change (%)                                                                          -40  -74   ±0 -10   +2                                    Compression set test [Evaluation]                                                              ∘                                                                      x     ∘                                                                       ∘                                                                       ∘                         (150° C. × 70 hrs)                                               Compression set (%)                                                                            28   76    38    17    18                                    Oil resistance (JIS No. 3) [Evaluation]                                                        ∘                                                                      ∘                                                                       ∘                                                                       ∘                                                                       ∘                         (150° C. × 70 hrs)                                               Hardness change (pts.)                                                                         -11  -8    -9    -9    ±0                                 Tensile strength change (%)                                                                    -21  -25   -19   -6    -1                                    Elongation change (%)                                                                          -14  -4    -15   +3    +2                                    Volume change (%)                                                                              +20  +11   +22   +20   +2                                    PAG resistance test [Evaluation]                                                               ∘                                                                      x     x     ∘                                                                       ∘                         (150° C. × 70 hrs.)                                              Hardness change (pts.)                                                                         -1   +8    -13   -2    -1                                    Tensile strength change (%)                                                                    -3   -28   -11   ±0 +3                                    Elongation change (%)                                                                          -7   -60   -8    +2    ±0                                 Volume change (%)                                                                              +5   -3    +26   +7    +1                                    Water resistance [Evaluation]                                                                  ∘                                                                      ∘                                                                       x     ∘                                                                       ∘                         (100° C. × 70 hrs.)                                              Hardness change (pts.)                                                                         +8   +2    -14   -1    -4                                    Tensile strength change (%)                                                                    +1   +1    -31   +3    -5                                    Elongation change (%)                                                                          +6   +2    +35   +3    +6                                    Volume change (%)                                                                              +16  +5    +32   +1    +9                                    Abrasion resistance test [Evaluation]                                                          ∘                                                                      ∘                                                                       x     ∘                                                                       .increment.                           Relative abrasion loss                                                                         100  82    212   53    121                                   Cost [Evaluation]                                                                              ∘                                                                      ∘                                                                       .increment.                                                                         x     x                                     Ratio            1    0.8   1.6   6     10                                    __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                     Test Example                                                                         Comparative Example                                   Component (weight parts)                                                                       2      5   6   7   8   9                                     __________________________________________________________________________            JSR N640H                                                                              100    100 100 100 100 100                                           Stearic acid                                                                           1      1   1   1   1                                                 Nocrac CD                                                                              2      2   2   2   2   2                                             Hydrozincite #1                                                                        --     --  --  --  5   5                                     Reinforc-                                                                             Nipsil ER                                                                              45     --  --  --  --  --                                    ing     Carplex #1120                                                                          --     --  --  --  45  --                                    filler  Carplex XR                                                                             --     45  --  --  --  --                                            SRF carbon                                                                             --     --  30  --  --  30                                            MT carbon                                                                              --     --  50  --  --  50                                            Satintone No.5                                                                         --     --  --  90  --  --                                    Vulcani-                                                                              Sulfur   --     --  --  --    0.5                                                                               0.5                                 zation  Accelerator TT                                                                         --     --  --  --  2   2                                     agent   Accelerator CZ                                                                         --     --  --  --  2   2                                             Percumyl D-40                                                                          3      3   3   3   --  --                                    Vulcani-                                                                              Kyowamag #150                                                                          10     10  10  10  --  --                                    zation  Calcium hydroxide                                                                      --     --  --  --  --  --                                    accele-                                                                       rator                                                                         KBM503           1      1   1   1   1   --                                    Plasticizer DOP  5      5   5   5   5   5                                     Vulcani-                                                                              Primary press                                                                          180° C.                                                                       180° C.                                                                    180° C.                                                                    180° C.                                                                    180° C.                                                                    180° C.                        zation  vulcanization                                                                          5 min  5 min                                                                             5 min                                                                             5 min                                                                             5 min                                                                             5 min                                 condi-  Secondary oven                                                                         150° C.                                                                       150° C.                                                                    150° C.                                                                    150° C.                                                                    --  --                                    tion    vulcanization                                                                          4 hrs  4 hrs                                                                             4 hrs                                                                             4 hrs                                         __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________                   Test Test Comparative                                                                         Comparative                                                                         Comparative                                                                         Comparative                                                                         Comparative                                 Example 1                                                                          Example 2                                                                          Example 5                                                                           Example 6                                                                           Example 7                                                                           Example 8                                                                           Example                      __________________________________________________________________________                                                     9                            Dry mechanical properties                                                     Hardness (JIS-A)                                                                             65   64   73    64    69    61    65                           Tensile strength (MPa)                                                                       15.03                                                                              17.81                                                                              18.41 16.80 12.48 14.00 13.85                        Elongation (%) 372  335  278   263   250   453   385                          Heat aging test [Evaluation]                                                                 ◯                                                                      Δ                                                                            X     X     X     X     X                            (heating in air 140° C. × 336 hrs)                               Hardness change (pts.)                                                                       +17  +18  +18   +24   +18   +26   +28                          Tensile strength change (%)                                                                  -19  -34  -39   -25   +15   -18   +21                          Elongation change (%)                                                                        -62  -70  -80   -85   -80   -83   -90                          Compression set test [Evaluation]                                                            ◯                                                                      ◯                                                                      ◯                                                                       ◯                                                                       ◯                                                                       X     ◯                (140° C. × 70 hrs)                                               Compression set (%)                                                                          24   24   30    21    23    59    30                           __________________________________________________________________________

EXAMPLES

Referring to the drawings, several examples in which the sealing memberaccording to the present invention is applied are now described.

In FIG. 1, the reference numeral 1 indicates an inner ring, 2 an outerring, 3 a ball, 4 a cage, and 5 and 6 each an oil seal. The oil seals 5and 6 are formed from a modified nitrile rubber according to the presentinvention, with the outside periphery thereof being fixedly mounted onthe outer ring 2 and the inside periphery being slidably in contact withthe inner ring 1 and having a metal case 8 therewithin. The internalclearance 7 is filled with, for example, a diurea type grease.

The roller bearing is not limited to the double row ball bearing shownin FIG. 1 but the present invention can be applied to single row ballbearings, needle roller bearings, cylindrical roller bearings and thelike as well.

FIG. 2 illustrates an example in which a sealing member according to thepresent invention is applied to a swash type rotary compressor. FIG. 3illustrates an example in which a sealing member according to thepresent invention is applied to an alternator bearing. FIG. 4illustrates an example in which a sealing member according to thepresent invention is applied to a water pump bearing. FIG. 5 illustratesan example in which a sealing member according to the present inventionis applied to a center bearing. FIG. 6 illustrates an example in which asealing member according to the present invention is applied to an axlebearing. FIG. 7 illustrates an example in which a sealing memberaccording to the present invention is applied to a tension pulleybearing. FIG. 8 illustrates an example in which a sealing memberaccording to the present invention is applied to a crank bearing. FIG. 9illustrates an example in which a sealing member according to thepresent invention is applied as a steering rod seal. FIG. 10 illustratesan example in which a sealing member according to the present inventionis applied to a bearing for a differential mechanism.

In Table 5 given below, comparisons were made among the electromagneticclutch bearing seal shown in FIG. 1, the alternater bearing seal shownin FIG. 3, the water pump bearing seal shown in FIG. 4, the wheelbearing seal shown in FIG. 6, the oil seal for reciprocating movementshown in FIG. 9 and a general oil seal for rotational motion (notillustrated), for each of which a sealing member of the presentinvention is used, on one hand and, on the other, those made of NBR,ACM, hydrogenated NBR or FKM which have hitherto used. The testconditions for the various application examples were as follows:

1) Electromagnetic clutch bearing seal: 140° C.×12,000 rpm×1,000 hours

2) Alternator bearing seal: 140° C.×18,000 rpm×1,000 hours

3) Water pump bearing seal: 120° C.×6,000 rpm×1,000 hours of sprayingwith the vapor of 50% aqueous solution of LLC (long life coolant)

4) Wheel bearing seal: 1,500 rpm×1,000 hours, muddy water (JIS 8-kinddust, 5% by weight)

5) Oil seal for reciprocating movement: 120° C.×80 kgf/cm² ×10⁴reciprocations

6) Oil seal for rotational motion: 130° C.×4,000 rpm×1,000 hours, gearoil (75w-90)

In Table 5, the following evaluation criteria are used:

∘: Good

Δ: Rather poor

X: Poor

                                      TABLE 5                                     __________________________________________________________________________            Test               Hydrogenated                                               Example 1                                                                          NBR    ACM    NBR    FKM                                         __________________________________________________________________________    Electromagnetic                                                                       ◯                                                                      X      ◯                                                                        --     --                                          clutch bearing                                                                             (bearing failure                                                 seal         revealed by                                                                   grease leakage                                                   Alternator                                                                            ◯                                                                      X      ◯                                                                        --     --                                          bearing seal (bearing failure                                                              revealed by                                                                   grease leakage                                                   Water pump                                                                            ◯                                                                      X      ◯                                                                        ◯                                                                        X                                           bearing seal (hardening and       (permanent set and                                       failure of lip)      failure of lip)                             Wheel bearing                                                                         ◯                                                                      ◯                                                                        X      ◯                                                                        ◯                               seal                (softening and                                                                failure of lip)                                           Oil seal for                                                                          ◯                                                                      Δ                                                                              --     ◯                                                                        --                                          reciprocating                                                                              (hardening of                                                    movement     lip and oil                                                                   leakage)                                                         Oil seal for                                                                          ◯                                                                      X      ◯                                                                        ◯                                                                        ◯                               rotational   (hardening of                                                    motion       lip and oil                                                                   leakage)                                                         __________________________________________________________________________

INDUSTRIAL APPLICABILITY

The present invention provides a sealing member which satisfactorily hasthose fundamental properties required thereof, namely sealing property,heat resistance, mechanical strength and oil resistance and is, inaddition, excellent in creep resistance and PAG resistance, since thesealing member is constituted by molding a modified nitrile rubber ofthe butadiene-acrylonitrile-acrylate type which contains an organicperoxide as a vulcanization agent, a metal oxide as a vulcanizationaccelerator, and a basic silicic acid as a reinforcing filler.

What is claimed is:
 1. A sealing member characterized by having anelastic part formed by molding a modified nitrile rubber of thebutadiene-acrylonitrile-acrylate type which contains an organic peroxideas a vulcanization agent, a metal oxide as a vulcanization acceleratorand a basic silicic acid as a reinforcing filler, wherein said basicsilicic acid is contained in an amount of 10 to 60 parts by weight per100 parts by weight of the modified nitrile rubber.
 2. The sealingmember according to claim 1, wherein said metal oxide is magnesiumoxide.
 3. The sealing member according to claim 1, wherein said metaloxide is contained in an amount of 5 to 20 parts by weight per 100 partsby weight of the modified nitrile rubber.
 4. The sealing memberaccording to claim 1, wherein said organic peroxide is dicumyl peroxide.5. The sealing member according to claim 1, wherein said organicperoxide is contained in an amount of 1 to 10 parts by weight per 100parts by weight of the modified nitrile rubber.
 6. The sealing memberaccording to claim 1 which has a metal case therewithin.
 7. A sealedbearing having a sealing member characterized in that said sealingmember has an elastic part formed by molding a modified nitrile rubberof the butadiene-acrylonitrile-acrylate type which contains an organicperoxide as a vulcanization agent, a metal oxide as a vulcanizationaccelerator and a basic silicic acid as a reinforcing filler, whereinsaid basic silicic acid is contained in an amount of 10 to 60 parts byweight per 100 parts by weight of the modified nitrile rubber.
 8. Thesealed bearing according to claim 7, wherein said metal oxide ismagnesium oxide.
 9. The sealed bearing according to claim 7, whereinsaid metal oxide is contained in an amount of 5 to 20 parts by weightper 100 parts by weight of the modified nitrile rubber.
 10. The sealedbearing according to claim 7, wherein said organic peroxide is dicumylperoxide.
 11. The sealed bearing according to claim 7, wherein saidorganic peroxide is contained in an amount of 1 to 10 parts by weightper 100 parts by weight of the modified nitrile rubber.
 12. The sealedbearing according to claim 7, wherein said sealing member has a metalcase therewithin.